Excel and Sheets habits that scale: when a file becomes a liability, real tables, keys, cleaning, clean exports, and a one-page table contract.
- 1 When a spreadsheet becomes a liability Spreadsheets start handy and can end as multiplayer systems of record with no owner. Learn the liability ladder, red flags, and Monday fixes before you trust a file with a real decision.
- 2 Tables, not freeform cells Headers once, one value per cell, tidy vs wide. Turn pretty spreadsheet layouts into analysis tables that filter, join, and export without drama.
- 3 Keys, IDs, and joining in plain English Why customer_id beats matching on names. Primary keys, foreign keys, one-to-many joins, and sheet habits that keep IDs stable.
- 4 Cleaning before you analyze (Sheets edition) A practical Sheets cleaning pass: trim, dates, splits, nulls, and deduping only after grain is clear. Keep raw copies; log your steps.
- 5 Exporting cleanly into SQL or a warehouse UTF-8 CSVs, honest types, ISO dates, no totals rows, and a handoff note so pipelines and people load what you meant to ship.
- 6 Your first table contract One page that records grain, keys, ownership, columns, exclusions, and allowed use so multiplayer tables stay trustworthy.